1. Field of Invention
The invention relates to working machinery, used for a variety of jobs in construction and civil engineering projects.
2. Description of Related Art
Generally, with some working machinery, such as hydraulic shovels, working attachments, such as a bucket, grapple and breaker, are selectively replaceable depending on the type of work to be done, e.g., excavation, loading and cracking. When an attachment mounted to, for example, the fore end of an arm of a hydraulic shovel is replaced, considerable labor and time are required because of the need to remove and insert pins which couple the arm and the attachment, and then securing the pins.
Hitherto, there is known an attachment mounting/demounting device 30 constructed to mount and demount an attachment with a hydraulic force, as shown in FIG. 9. The attachment mounting/demounting device 30 is made up of a bracket 33 supported to the arm side through first and second support pins 31, 32, a rocker arm 34 supported by the second support pin 32 in a rockable manner, and a hydraulic cylinder 35 interposed between the rocker arm 34 and the bracket 33. The bracket 33 and the rocker arm 34 have engagement grooves 33a, 34a formed to be engageable with first and second pins 7a, 7b fixed to the attachment side, respectively. In a condition where the first pin 7a is held in engagement with the engagement groove 33a of the bracket 33, the hydraulic cylinder 35 is extended to make the second pin 7b engaged with the engagement groove 34a of the rocker arm 34, whereby the attachment is mounted to the mounting/demounting device 30. On the other hand, by contracting the hydraulic cylinder 35 to disengage the second pin 7b from the engagement groove 34a of the rocker arm 34, the attachment can be removed from the mounting/demounting device 30.
In the above conventional mounting/demounting device, there is a risk that the pin may be disengaged from the engagement groove when the attachment is mounted and being used, if a larger load than expected is imposed on the contraction side of the hydraulic cylinder or if a check valve for restricting the contraction of the hydraulic cylinder should fail to function. To counter, and prevent, such an event from happening, some devices are constructed to mechanically lock the pin, which is held in engagement with the engagement groove, by using a lock member such a lock bolt or lock pin. These devices however require the work of mounting or demounting the bolt or pin to lock or unlock the lock member, thus resulting in a problem that the mounting and demounting work is troublesome and laborious.
To overcome the above problem, as disclosed in Japanese Unexamined Patent Publication No. 9-209391, a latch is provided which is capable of switching over between a release posture allowing the pin to come into and out of the engagement groove and an engagement posture preventing slip-off of the pin fitted to the engagement groove. The latch is rocked between the release posture and the engagement posture with the extending and contracting operation of the hydraulic cylinder which serves also to angularly move the rocker arm.
In the above related art, the latch is set to preclude switching over to the release posture even if the pin is subjected to a force acting on the pin that would normally cause the pin to disengage from the engagement groove in the event of a failure of the hydraulic cylinder or of the hydraulic circuit. However, if the latch itself, which is held in the engagement posture, strikes against an obstacle, for example, so as to produce a force acting on the latch to rock into the release posture, there is a possibility that the latch may release. For this reason, more reliable measures are required to ensure safety.